The present invention relates to reliably and accurately detecting, decoding and recovering data pulses that have been added to a signal. In one particular use, the invention relates to detecting, decoding and recovering structural information which informs a DVD recording system of certain parameters required to effect write operations, such as what laser power level to use and address information identifying location information on the media, wherein the information has been stored in land pre-pits (LPPs). The example of DVD media and LPPs is used herein to provide background and also to illustrate an exemplary embodiment. For the purposes of this application, the terms given in Definition List 1, below, have the meanings given.
Definition List 1TermDefinitionDetectingIdentifying signal componentsrepresenting LPP data and interpretingidentified signal components asparticular LPP symbols.DecodingExtracting meaning from detected LPPsymbols.
Information is recorded on a surface of DVD-R/RW media on a track, 100, defined by a spiral groove, 101, bounded by raised areas called lands, 102, 103. (See FIG. 1.) User information is written in the groove, 101, as a series of marks and spaces defined by regions of high and low relative reflectivity. The lands, 102, 103, that bound the grooves include features R1, R2, R3, 104, 105, that represent certain address information and medium-related parameters, such as the power required to read and/or write the user information.
The spiral groove, 101, defined by the lands, 102, 103, follows a spiral path on which is superimposed a substantially sinusoidal, radial wobble (R1, R2, R3, for example) having a constant wavelength, λ, where λ is measured as distance along the track. In systems where the medium rotational speed is controlled to a constant linear velocity along the entire track, the recovered wobble signal has a fixed frequency, which is scaled with the linear velocity. The system uses the wobble as a scale or ruler that represents distances along the track by numbers of cycles of the fixed wavelength, λ. Thus, read and write clocks and disk rotation speed control may all be derived from the frequency of the recovered sinusoidal wobble signal. For example, in DVD-R/RW media the timing of information within read and write signals is defined by channel bits of duration T, and the wobble wavelength is defined to be 186T. Other media may use other relationships.
In addition, superimposed on the wobble at predetermined, fixed locations relative to the phase of the sinusoidal wobble are microscopic pits formed in the lands during the manufacture of the disk substrate, called land pre-pits (LPP), 104, 105. Conventional DVD-R/RW media sets the locations at 0°+/−10° from peaks (+/−) of the wobble, for example as seen in FIG. 2. Sector synchronization information and other disk specific information is identified by the locations of certain predetermined sequences of LPPs, 104, 105. Short sequences of LPPs, referred to herein as LPP symbols, are defined by the following Table, in which each LPP symbol is comprised of three bits identified as b0, b1, and b2. Here, a “1” indicates that an LPP spike, as defined below, is detected at the location of the indicated bit and a “0” indicates that an LPP spike is not detected at the location of the indicated bit. Sequences of LPP symbols manufactured into the media have more complex meanings.
TABLEDefinitionb2b1b0EVEN SYNC111ODD SYNC110Pre-pit DATA ONE101Pre-pit DATA ZERO100
The features defining the tracks, including the lands, the grooves and the LPPs may be embossed or otherwise formed on the media together, at the time of manufacture.
The wobble signal is recovered using a four-quadrant photo detector, whose analog signal outputs are then combined algebraically by any suitable analog or digital signal processing to form the radial push-pull signal. While the head is following a track, the radial push-pull signal is the substantially sinusoidal wobble signal, 201. (See FIG. 2.) When the head passes over an LPP, a spike, 202, is superimposed on the substantially sinusoidal wobble signal. LPPs are located at positions, 203, corresponding to peaks of the sinusoidal wobble always having the same polarity (+/−). Thus, the LPP spikes 202 are data pulses added to the underlying wobble signal 201 at particular locations.
The meaning of the sequence of LPPs is determined by detecting LPP symbols comprised of sequences of the presence or absence of the spikes on the wobble signal at particular locations, and decoding the sequence symbols into more complex meanings.
As indicated above, LPP information is embossed or otherwise prerecorded on DVD-R/RW media, other than when a user records data, for example during manufacture. The prerecorded LPP information carries various information used during subsequent recording of user data on the DVD-R/RW media. In order to successfully record user data in a manner permitting subsequent reliable recovery, the LPP spikes must be reliably detected. The amplitudes of the LPP spikes appearing on the wobble signal depend on many factors. The large number of factors which can vary the amplitudes of the LPP spikes tend to make a precise prediction of the average LPP spike amplitude difficult. Among the many factors, one important factor is significant variation in the amplitude of the quadrant photo detector signal output, especially variation in amplitude between different operating modes, such as between reading, erasing and writing operations. Laser power levels are highest during the write operation and lowest during the read operation. Due to the way DVD-RW media behaves while being erased, additional variations occur in optical pickup output as DVD-RW media traverses from the recorded to the erased state.
In order to reliably extract LPP information from the push-pull signal, conventional approaches preset a slice level, 204, using a digital-to-analog converter (DAC). The conventional preset slice level, 204, substantially splits the difference between the peak LPP spike amplitude, 205, and the peak amplitude of the single-frequency sinusoid of the wobble signal, 206, absent the LPP spikes. Assuming an n-bit DAC is used to set the slice level, 204, the slice level, 204, can take on any of 2n possible values.
United States Patent Application 2005-0002304, Lo et al., discloses one implementation of the described conventional art, which uses a bottom hold value to deduce a slice level.
U.S. Pat. No. 6,801,488, Kato et al., discloses a method to determine the slice level based on a set of computations related to LPP spike amplitude.
U.S. Pat. No. 6,757,233 discloses opening a gate only in the period during which the amplitude of the wobbling becomes a maximum. LPPs are detected during the gated interval.